Diffusion ejector pump



Sept. 22, 1959 T. L. SCATCHARD DIFFUSION EJECTOR PUMP Filed Feb 10, 1958OOOOOOOQOMQO0000O00OOOOOQWOOOOOOOOOOOQ INVENTOR. ThomasLScatchard A'Horneys United States Patent DIFFUSION EJECTOR PUMP Thomas L. Scatchard,Philadelphia, Pa., assignor to The lJYew York Air Brake Company, acorporation of New ersey Application February 10, 1958, Serial No.714,176

3 Claims. (Cl. 230-101) This invention relates .to vapor vacuum pumpsand more particularly to diffusion-ejector pumps.

The object of this invention is to provide a diffusionejector pumphaving a higher throughput (i.e., volume of gas pumped per unit of timemultiplied by the pressure of the gas) over a wider pressure rangethan-similar devices of the prior art while at the same time being morecompact. According to the invention, the ejector nozzle comprises anannular opening in a toroidal chamber surrounding the jet chimney whichtransmits pumping vapors to the diffusion pumping stages. The ejectornozzle discharges into the entrance of an annular diffuser nozzle whichis spaced from the ejector nozzle to define an intervening annularentraining area in communication with anannular discharge passageleading from the diffusion pump section. This arrangement of elementsresults in a compact structure affording a large entraining area for theejector nozzle.

A further feature of the invention is the provision of means to vary thethroat area of both the ejector nozzle and the diffuser nozzle. In priorpumps having fixed throat areas, the minimum pressure which could beestablished by the pump was limited by the backstreaming of vapormolecules toward the inlet. This is attributable to the fact that as thepressure in the system being evacuated decreased, the rate ofbackstreaming increased, and when it equaled the throughput of gas,pumping action ceased. This condition could be improved somewhat byvarying the energy input to the heater of the vapor boiler as thepressure dropped, but due to the heat capacity of the pump, thisprocedure was of little help when rapid fluctuations in system pressurewere encountered. Furthermore, in this type of pump the dimensions ofthe throat of the diffuser nozzle should be of the same order ofmagnitude as the mean free path of the gas molecules at this point. Ifthe throat is too large the pump will have poor fore pressure tolerance;if it is too small the throughput of gas will be reduced. Since thethroat area was fixed and since mean free path varies with pressure, thedesign of the diffuser represented a compromise. In accordance with thisinvention, the velocity and entraining area of the ejector jet streamcan be varied rapidly in accordance with either fore pressure, or inletpressure, or both, to afford maximum throughput for the prevailingoperating conditions.

Referring to the drawing, which is an axial section of a preferredembodiment of the invention, the pump comprises a cylindrical casing 1having a flanged inlet p assage or port 2 and a plurality ofcircumferentially spaced outlet passages 3. In the bottom of the casingare located two electrically heated concentric vapor boilers 4 and 5;the inner boiler 4 feeding a cylindrical jet chimney 6 and the outerboiler 5 feeding a toroidal chamber 7. The chimney 6 is closed by aconical cap 8 and is provided with three longitudinally spaced series ofjet openings 9. Associated with each series is a jet skirt 11 formed inthe shape of a thin-walled truncated cone and "ice 2 arranged to directpumping vapors issuing from openings 9 toward the outlet passages 3.

The outer wall of toroidal chamber 7 consists of a fixed portion 12 anda movable portion 13 which slides on chimney 6. Between the two portionsof the outer wall is an annular opening 14 which, together with thewall, constitutes an annular ejector nozzle. Aligned with but spacedfrom annular opening 14 is an encircling annular diffuser nozzle 15formed by a fixed wall 16 and a movable wall 17 which is guided by ring18. The annular area 19 between toroidal chamber 7 and nozzle 15constitutes the entraining area of the ejector nozzle. Communicatingwith the exit of the diifuser nozzle 15 and with outlet passages 3 is anoutlet manifold 21 in which is mounted an annular baflle 22.

A cooling coil 23 surrounds the casing 1. Those pumping vapors whichcondense on the walls of casing 1 upstream of the ejector nozzle,gravitate to annular trough 24 from which they are returned to innerboiler 4 by return line 25. Those vapors condensing downstream of thisnozzle accumulate in manifold 21 and in the space between toroidalchamber 7 and easing 1 and are returned to the outer boiler 5 by returnlines 26 and 27.

The movable walls of both the ejector nozzle 14 and the diffuser nozzle15 are actuated by electric motors 28 and 28 through lead screws 29, 29, 31 and 31'. Between motors 28 and 28 and their associated gearing arelocated transmissions 32 and 32' which, depending on the type of controldesired, can transmit power to either or both lead screws. In this way,the throat areas of the two nozzles can be varied simultaneously orindividually.

In operation, gas molecules from the system being evacuated will enterinlet passage 2, and diffuse through the vapor jet streams issuing fromopenings 9 and skirts 11. The vapor molecules will condense on thecooled walls of housing 1 and be returned to inner boiler 4. The gasmolecules, on the other hand, will be directed to the annular entrainingarea 19 of the ejector nozzle 14. The vapors issuing from annularejector nozzle 14 will entrap the gas molecules and carry them throughthe diffuser nozzle 15 to outlet manifold 21 from whence they will bewithdrawn by a fore pump through outlet passages 3. The vapors from theejector nozzle which condense on the walls of the diffuser nozzle 15 andmanifold 21 will be returned to the outer boiler 5. The dual boiler andcondensate return system makes it possible to use two different oils orto use the same oil at two different pressures. In this way, optimumoperating conditions can be closely approximated.

The electric motors 28 and 28' are controlled by a circuit whichresponds to changes in inlet pressure. When this pressure is high, themotors are operated to reduce the throat areas of nozzles 14 and 15 andthus provide a high velocity jet capable of producing a high throughputat this pressure. As the inlet pressure decreases, the motors willoperate in the reverse direction to increase the areas of the twothroats and thus increase the volume of gas being pumped. The net resultis that the throughput is maintained substantially constant over a largerange of pressures.

In lieu of this inlet pressure control, the motors could be controlledin accordance with changes in fore pressure. As in the previous case,the throat areas would be varied in inverse relation to the pressure. Acombined fore pressure and inlet pressure control could also be used.

As stated previously, the drawing and description relate only to apreferred embodiment of the invention. Since many changes can be made inthis embodiment without departing from the inventive idea, the followingclaims should provide the sole measure of the scope of the invention.

What is claimed is:

1. A diffusion-ejector pump comprising a cylindrical casing; twoconcentricvapor boilers located at one end of the casing; an inlet portformed in the casing at its opposite end; a cylindrical jetchimney-connectedwith the inner boiler; at least one difiusion.pump'nozzle fed by the chimney and arranged to discharge pumping'vaporsin a direction away from the inlet port; a housing defining a toroidalchamber surrounding the chimney and connected with the outer boiler,said chamber being located downstream of the diffusion pump nozzle; anencircling opening in the outer periphery of the housing,

issuing from the diffusion pump nozzles and the annular ejector nozzlemay condense; a first condensate drain located in thecasing upstream ofthe annular ejector nozzle and connected with the inner boiler forcollecting and returning to that boiler those vapors which condense onthe cooled casing; and a second condensate drain located downstream ofthe annular ejector nozzle and connected with the outer boiler forcollecting and returning to that boiler those vapors which condense onthe cooled diffuser nozzle.

2. The diffusion-ejector pump defined in claim 1 in which the housingdefining the toroidal chamber includes a movable wall which is shiftablein opposite directions to vary the throat area of the annular ejectornozzle; in which the annular difiuser nozzle includes a movable wallwhich is shiftable in opposite directions to vary the throat area of thediifuser nozzle; and including actuating means connected with themovable housing wall for shifting it in said opposite directions, andactuating means connected with the movable diffuser wall for shifting itin said opposite directions.

3. A diffusion-ejector pump comprising a casing having an inlet and anoutlet; a jet chimney located within and spaced from the casing; atleast one diffusion pump nozzle located downstream of the inlet andarranged to direct vapors supplied by the chimney toward the outlet; apumping vapor boiler connected with the chimney; a housing defining atoroidal chamber surrounding the chimney and located downstream-of thediflfusion pump nozzle; an auxiliary boiler connected with the toroidalchamber; an encircling opening in the outer'periphery of the housing,said opening and the walls of the housing cooperating to form an annularejector nozzle; an annular difiuser nozzle encircling theejector nozzle,the entrance of the diffuser nozzle being aligned with but spaced fromthe ejector nozzle to define an intervening annular entraining area; andan outlet manifold connected with the exit of the diiiuser nozzle andwith the outlet.

References Cited in the file of this patent UNITED STATES PATENTS2,361,245 Stallmann n. Oct. 24, 1944

